US10080240B2 - Method and apparatus for transmitting frame in wireless LAN - Google Patents

Method and apparatus for transmitting frame in wireless LAN Download PDF

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US10080240B2
US10080240B2 US15/119,346 US201415119346A US10080240B2 US 10080240 B2 US10080240 B2 US 10080240B2 US 201415119346 A US201415119346 A US 201415119346A US 10080240 B2 US10080240 B2 US 10080240B2
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frame
sta
cts
rts
transmitted
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US20170013645A1 (en
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Jinsoo Choi
Kiseon Ryu
Wookbong Lee
Jinyoung Chun
Dongguk Lim
HanGyu CHO
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LG Electronics Inc
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LG Electronics Inc
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Assigned to LG ELECTRONICS INC. reassignment LG ELECTRONICS INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHUN, JINYOUNG, CHO, HANGYU, CHOI, JINSOO, LIM, DONGGUK, RYU, KISEON, LEE, WOOKBONG
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
    • H04W74/0816—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA] with collision avoidance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/06—TPC algorithms
    • H04W52/14—Separate analysis of uplink or downlink
    • H04W52/143—Downlink power control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0453—Resources in frequency domain, e.g. a carrier in FDMA
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access
    • H04W74/0841—Random access procedures, e.g. with 4-step access with collision treatment
    • H04W74/085—Random access procedures, e.g. with 4-step access with collision treatment collision avoidance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/10—Small scale networks; Flat hierarchical networks
    • H04W84/12—WLAN [Wireless Local Area Networks]

Definitions

  • the present invention relates to wireless communication and, most particularly, to a method and apparatus for transmitting a frame in a wireless LAN.
  • the range of channel bandwidths that are available for usage in the legacy wireless LAN system has become diverse from 20 MHz to 160 MHz. Accordingly, deciding an adequate channel bandwidth for the communication between a transmitting user equipment and a receiving user equipment has become a crucial factor in determining Wi-Fi performance.
  • a dynamic channel bandwidth configuration protocol which is based on a RTS(request to send) frame and a CTS(clear to send) frame, has been developed starting from IEEE 802.11ac.
  • the initial RTS frame and CTS frame have been devised to resolve the hidden node issue and to reduce data frame collision overhead.
  • the transmitting user equipment Before transmitting a data frame, the transmitting user equipment transmits a RTS frame to the receiving user equipment. After receiving the RTS frame, the target user equipment sends a response to the transmitting user equipment by using the CTS frame.
  • Third party user equipments that have received the RTS frame and the CTS control frame may delay medium access for a predetermined period of time for the protection of data frame that are to be transmitted later on.
  • the transmitting user equipment may transmit a RTS frame through a wide band exceeding a channel bandwidth of 20 MHz, and the target user equipment may send a response with a CTS frame in accordance with a channel bandwidth that can be currently used by the corresponding target user equipment.
  • the RTS frame is transmitted through a 160 MHz channel bandwidth.
  • the target user equipment transmits the CTS frame through a 80 MHz channel bandwidth.
  • the transmitting user equipment that has transmitted the RTS frame receives a CTS frame through a channel bandwidth of 80 MHz
  • the data frame that is transmitted afterwards to the target user equipment by the transmitting user equipment should be equal to or smaller than the 80 MHz channel bandwidth.
  • An object of the present invention is to provide a method for transmitting a frame in a wireless LAN.
  • Another object of the present invention is to provide an apparatus performing a method for transmitting a frame in a wireless LAN.
  • a method for transmitting a frame in a wireless LAN may include the steps of transmitting, by an AP(access point), a RTS(request to send) frame for medium protection to a first STA(station) group, sequentially receiving, by the AP, CTS(clear to send) frames from each of multiple STAs being included in a second STA set as a response to the RTS frame, wherein the second STA set is included in the first STA set, and respectively transmitting, by the AP, each of multiple PPDUs (physical layer protocol data unit) to each of the multiple STAs through each of multiple subbands for each of the multiple STAs within an overlapping time resource.
  • PPDUs physical layer protocol data unit
  • an AP(access point) transmitting a frame in a wireless LAN may include a RF(radio frequency) unit being configured to transmit or receive radio signals, and a processor being operatively connected to the RF unit, wherein the processor may be configured to transmit a RTS(request to send) frame for medium protection to a first STA(station) group, to sequentially receive CTS(clear to send) frames from each of multiple STAs being included in a second STA set as a response to the RTS frame, and to respectively transmit each of multiple PPDUs (physical layer protocol data unit) to each of the multiple STAs through each of multiple subbands for each of the multiple STAs within an overlapping time resource, and wherein the second STA set may be included in the first STA set.
  • a RF(radio frequency) unit being configured to transmit or receive radio signals
  • a processor being operatively connected to the RF unit, wherein the processor may be configured to transmit a RTS(request to send) frame for medium protection to
  • the communication efficiency may be enhanced.
  • FIG. 1 illustrates a concept diagram illustrating the structure of a wireless local area network (WLAN).
  • WLAN wireless local area network
  • FIG. 2 illustrates a concept diagram showing a method for using a RTS frame and a CTS frame for resolving a hidden node issue and an exposed node issue.
  • FIG. 3 illustrates a concept diagram showing a CTS-to-Self Mechanism.
  • FIG. 4 illustrates a concept diagram showing a medium protection method when performing OFDMA communication based communication in a wireless LAN according to an exemplary embodiment of the present invention.
  • FIG. 5 illustrates a concept diagram of a RTS frame according to an exemplary embodiment of the present invention.
  • FIG. 6 illustrates a concept diagram showing a collision between a BSS supporting DL MU OFDMA transmission and a BSS not supporting DL MU OFDMA transmission.
  • FIG. 7 illustrates a concept diagram showing a collision between a BSS supporting DL MU OFDMA transmission and a BSS not supporting DL MU OFDMA transmission.
  • FIG. 8 illustrates a medium protection method according to an exemplary embodiment of the present invention.
  • FIG. 9 illustrates a medium protection method according to an exemplary embodiment of the present invention.
  • FIG. 10 illustrates a concept diagram of a downlink frame being transmitted based on DL MU OFDMA according to an exemplary embodiment of the present invention.
  • FIG. 11 illustrates a concept diagram of a downlink frame being transmitted based on DL MU OFDMA according to an exemplary embodiment of the present invention.
  • FIG. 12 illustrates a concept diagram of a downlink frame being transmitted based on DL MU OFDMA according to an exemplary embodiment of the present invention.
  • FIG. 13 illustrates a concept diagram showing a downlink frame transmission method of an AP according to an exemplary embodiment of the present invention.
  • FIG. 14 illustrates a concept diagram showing a PPDU format for transmitting a frame according to an exemplary embodiment of the present invention.
  • FIG. 15 illustrates a block diagram showing a wireless communication system in which the disclosure of this specification is implemented.
  • FIG. 1 illustrates a concept diagram illustrating the structure of a wireless local area network (WLAN).
  • WLAN wireless local area network
  • FIG. 1 shows the structure of the IEEE(institute of electrical and electronic engineers) 802.11 infrastructure network.
  • the WLAN system may include one or more basic service sets (BSSs, 100 and 105 ).
  • the BSS 100 or 105 is a set of an AP such as AP (access point) 125 and an STA such as STA 1 (station) 100 - 1 that may successfully sync with each other to communicate with each other and is not the concept to indicate a particular area.
  • the BSS 105 may include one AP 130 and one or more STAs 105 - 1 and 105 - 2 connectable to the AP 130 .
  • the infrastructure BSS may include at least one STA, APs 125 and 130 providing a distribution service, and a distribution system (DS) 110 connecting multiple APs.
  • STA station-to-live
  • APs 125 and 130 providing a distribution service
  • DS distribution system
  • the distribution system 110 may implement an extended service set (ESS) 140 by connecting a number of BSSs 100 and 105 .
  • ESS 140 may be used as a term to denote one network configured of one or more APs 125 and 230 connected via the distribution system 110 .
  • the APs included in one ESS 140 may have the same SSID (service set identification).
  • the portal 120 may function as a bridge that performs connection of the WLAN network (IEEE 802.11) with other network (for example, 802.X).
  • IEEE 802.11 IEEE 802.11
  • a network between the APs 125 and 130 and a network between the APs 125 and 130 and the STAs 100 - 1 , 105 - 1 , and 105 - 2 may be implemented.
  • a network may be established between the STAs to perform communication.
  • the network that is established between the STAs without the APs 125 and 130 to perform communication is defined as an ad-hoc network or an independent BSS (basic service set).
  • FIG. 1 A lower portion of FIG. 1 is a concept view illustrating an independent BSS.
  • the independent BSS is a BSS operating in ad-hoc mode.
  • the IBSS does not include an AP, so that it lacks a centralized management entity.
  • the STAs 150 - 1 , 150 - 2 , 150 - 3 , 155 - 1 , and 155 - 2 are managed in a distributed manner.
  • all of the STAs 150 - 1 , 150 - 2 , 150 - 3 , 155 - 1 , and 155 - 2 may be mobile STAs, and access to the distribution system is not allowed so that the IBSS forms a self-contained network.
  • the STA is some functional medium that includes a medium access control (MAC) following the IEEE (Institute of Electrical and Electronics Engineers) 802.11 standards and that includes a physical layer interface for radio media, and the term “STA” may, in its definition, include both an AP and a non-AP STA (station).
  • MAC medium access control
  • the STA may be referred to by various terms such as mobile terminal, wireless device, wireless transmit/receive unit (WTRU), user equipment (UE), mobile station (MS), mobile subscriber unit, or simply referred to as a user.
  • WTRU wireless transmit/receive unit
  • UE user equipment
  • MS mobile station
  • a user or simply referred to as a user.
  • FIG. 2 illustrates a concept diagram showing a method for using a RTS frame and a CTS frame for resolving a hidden node issue and an exposed node issue.
  • a short signaling frame such as a request to send (RTS) frame, a clear to send (CTS) frame, or the like may be used.
  • RTS request to send
  • CTS clear to send
  • Neighboring STAs may know whether to transmit or receive data between two STAs on the basis of the RTS frame and the CTS frame.
  • FIG. 2(A) illustrates a method of transmitting an RTS frame 203 and a CTS frame 205 to solve a hidden node issue.
  • the STA A 200 may transmit the RTS frame 203 to the STA B 210 before transmission of the data frame, and the STA B 210 may transmit the CTS frame 205 to the STA A 200 .
  • the STA C 220 may overhear the CTS frame 205 , and may know frame transmission from the STA A 200 to the STA B 210 through a medium.
  • the STA C 220 may configure a network allocation vector (NAV) until the end of data frame transmission from the STA A 200 to the STA B 210 .
  • NAV network allocation vector
  • FIG. 2(B) illustrates a method of transmitting an RTS frame 233 and a CTS frame 235 to solve an exposed mode issue.
  • An STA C 250 may determine whether a collision occurs when a frame is transmitted to another STA D 260 on the basis of monitoring of the RTS frame 233 and CTS frame 235 of an STA A 230 and an STAB 240 .
  • the STA B 240 may transmit the RTS frame 233 to the STA A 230 , and the STA A 230 may transmit the CTS frame 235 to the STA B 240 .
  • the STA C 250 overhears only the RTS frame 233 transmitted by the STA B 240 , and fails to overhear the CTS frame 235 transmitted by the STA A 230 . Therefore, the STA C 250 may know that the STA A 230 is located out of a carrier sensing range of the STA C 250 . Accordingly, the STA C 250 may transmit data to the STA D 260 .
  • RTS frame format and a CTS frame format are disclosed in the 8.3.1.2 RTS frame format and 8.3.1.3 CTS frame format of IEEE P802.11-REVmcTM/D2.0, October 2013.
  • FIG. 3 illustrates a concept diagram showing a CTS-to-Self Mechanism.
  • FIG. 3 a comparison between a case of sensing a medium by using an exchange method between a RTS frame and a CTS frame ((A) of FIG. 3 ) and a case of sensing a medium by using a CTS-to-Self frame ((B) of FIG. 3 ).
  • a CTS-to-self protection mechanism is defined in the IEEE 802.11g specification.
  • the CTS-to-self protection mechanism may be used instead of the medium sensing mechanism, which uses a RTS frame and a CTS frame.
  • the overhead of the medium may be reduced as compared to when using the medium sensing mechanism, which uses RTS/CTS frames.
  • the method for exchanging the RTS frame and the CTS frame before the transmitting end transmits the data frame may be performed as described below.
  • STA A 300 transmits a RTS frame 320 .
  • the RTS frame 320 is received by STA B 305 and STA C 310 , which is exist in a carrier sensing range.
  • STAB 305 and STA C 310 transmit CTS frames 325 and 330 .
  • the transmitted CTS frames 325 and 330 are transmitted to STA A 300 , STA B 305 , STA C 310 , and STA D 315 .
  • STA D 315 In case of STA D 315 , since STA D 315 exists outside of the carrier sensing range of STA A 300 , STA D 315 was unable to receive the RTS frame 320 transmitted by STA A 300 (i.e., STA D 315 is a hidden node of STA A 300 ). Nevertheless, by receiving the CTS frame 330 transmitted by STA C 310 , it will be apparent that STA A 300 has occupied the medium in order to transmit data. STA D may configure a NAV and may not access the medium.
  • STA A 300 transmits a data frame to STA C 310 .
  • a CTS-to-self frame based medium sensing method which is performed before the transmitting end transmits the data frame, may be performed as described above.
  • (B) of FIG. 3 a case when STA A 300 attempts to send a data frame to STA C 360 will be assumed.
  • STA A 350 transmits a CTS-to-self frame 370 , which exists in the carrier sensing range, to STAB 355 and STA C 360 .
  • STA B 355 and STA C 360 After receiving the CTS-to-self frame 370 , STA B 355 and STA C 360 delay the transmitted of another data frame in order to receive the data frame that is being transmitted from the STA A 350 .
  • STA D 365 which exists outside of the coverage region of STA A 350 , in unable to receive the CTS-to-self frame 370 from STA A 350 . Therefore, STA D 365 cannot know whether or not the data frame has been transmitted by STA A 350 .
  • method of using a CTS-to-self frame 370 may be applied only to the case when the STAs are capable of sensing the data frame transmission occurring between one another, and, in other cases, the medium may be sensed by using the method of exchanging RTS/CTS frames.
  • An AP(access point) that operates in a wireless local area network (WLAN) system may transmit different sets of data to each of the multiple STAs(stations) through the same (or overlapping) time resource. If the transmission from the AP to the STA is referred to as a downlink transmission, such transmission of the AP may be expressed by using the term DL MU transmission (or downlink multi-user transmission).
  • WLAN wireless local area network
  • the AP was capable of performing DL MU transmission based on MU MIMO(multiple input multiple output), and such transmission may be expressed by using the term DL MU MIMO transmission.
  • the AP may perform DL MU transmission based on OFDMA(orthogonal frequency division multiplexing access), and such transmission may be expressed by using the term DL MU OFDMA transmission.
  • the AP may transmit a downlink frame to each of the multiple STAs through each of the multiple frequency resources within the overlapping time resource.
  • the PPDU may correspond to a data unit including a PPDU header and a PDSU(physical layer service data unit) (or MPDU(MAC protocol data unit)).
  • the PPDU header may include a PHY header and a PHY preamble, and the PDSU (or MPDU) may include a frame or may indicate a frame.
  • the transmission from the STA to the AP may be referred to as an uplink transmission.
  • the data transmission of multiple STAs to the AP within the same (or overlapping) time resource may be expressed by using the term UL MU transmission (or uplink multi-user transmission).
  • the UL MU transmission may be supported in the wireless LAN system according to the exemplary embodiment of the present invention.
  • Each of the PPDU, frame, and data being transmitted via uplink transmission may be respectively expressed by using the terms uplink PPDU, uplink frame, and uplink data.
  • the uplink transmission performed by each of the multiple STAs may be respectively performed within different frequency domains (subbands) or within different spatial domains.
  • different frequency resources respective to each of the multiple STAs may be allocated as the uplink transmission resource based on OFDMA.
  • Each of the multiple STAs may respectively transmit an uplink frame to the AP through each of the different frequency resources allocated thereto.
  • Such transmission method using different frequency resources may also be expressed by using the term UL MU OFDMA transmission method.
  • each of the multiple STAs may be performed within different spatial domains.
  • different space time streams may be allocated with respect to each of the multiple STAs.
  • Each of the multiple STAs may respectively transmit an uplink frame to the AP through different space time streams.
  • Such transmission method using different space time streams may also be expressed by using the term UL MU MIMO transmission method.
  • next generation wireless LAN demands for high throughput and enhanced QoE(quality of experience) are increasing.
  • the design of a new system should be realized without any performance impact from legacy STAs, which support only the legacy wireless LAN system.
  • the next generation wireless LAN system is also required to be designed not to be influenced by any performance impact caused by the presence of a legacy STA.
  • the DL MU OFDMA transmission was not supported in the legacy (or conventional) wireless LAN system.
  • a wider bandwidth based on multi-channels was allocated for the communication between one STA and one AP.
  • the multi-channel may correspond to a bandwidth exceeding 20 MHz and including a primary channel and a secondary channel.
  • the STA may perform communication through the multi-channel including the secondary channel only in a case when the secondary channel is idle. More specifically, in case the secondary channel, which is adjacent to the primary channel, is being used in an OBSS(overlapped BSS) (i.e., in case the secondary channel is busy), the bandwidth cannot be expanded to a multi-channel, and the STA may perform communication only through the primary channel STA. In case the primary channel rule is being applied, it may be difficult to operate a wider bandwidth in an environment having more than a few OBSSs.
  • the usage efficiency of the frequency resource may be increased.
  • the OFDMA subband granularity may correspond to a subband (or frequency resource) unit being allocated for the communication of one STA.
  • a problem may occur in the co-existence of the legacy STA, which is operated based on the legacy 20 MHz frequency band, and the STA, which supports DL MU OFDMA communication, and which is operated based on a frequency band less than 20 MHz.
  • a problem may occur with respect to medium protection (or channel protection) based on a RTS frame and a CTS frame.
  • the RTS frame (or PPDU) or the CTS frame (CTS PPDU) may maintain the conventional (or legacy) frame format or (PPDU format).
  • the exemplary embodiment of the present invention discloses a medium protection method that is based on the RTS frame and CTS frame in an environment where a legacy STA and an STA supporting the next generation wireless LAN system co-exist.
  • the legacy STA may correspond to an STA that can be operated within a multi-channel of a 20 MHz bandwidth unit, which is decided based on the primary channel rule.
  • the STA supporting the next generation wireless LAN system may also be operated within a subband less than 20 MHz (or a subband of 20 MHz or more) based on DL MU OFDMA or UL MU OFDMA.
  • the STA may refer to an STA supporting the next generation wireless LAN system.
  • the OFDMA subband granularity is assumed. More specifically, one STA may perform communication with the AP based on a minimum subband of 5 MHz. Nevertheless, communication based on DL MU OFDMA and/or UL MU OFDMA, which is based on an OFDMA subband granularity of 20 MHz or less or 20 MHz or more, instead of 5 MHz, may also be performed.
  • the medium protection method based on the RTS frame/CTS frame may also be used in a case when a downlink frame (or downlink PPDU) is respectively transmitted to each of the multiple STAs by the AP through different space time streams based on DL MU MIMO.
  • FIG. 4 illustrates a concept diagram showing a medium protection method when performing OFDMA communication based communication in a wireless LAN according to an exemplary embodiment of the present invention.
  • FIG. 4 discloses a method of sequentially transmitting CTS frames 410 , 420 , 430 , and 440 in response to a RTS frame 400 .
  • the AP may transmit a RTS frame 400 to multiple STAs configuring an OFDMA packet.
  • the AP may transmit a RTS frame 400 to each of the multiple STAs, which are to respectively transmit multiple downlink frames, based on the DL MU OFDMA transmission.
  • each of the multiple STAs configuring an OFDMA packet each of the multiple STAs that are to be respectively receive each of the downlink frames, which are transmitted by the AP based on DL MU OFDMA transmission, may be expressed by using the term DL MU target STA.
  • the RTS frame 400 may include identification information respective to each of the multiple DL MU target STAs (e.g., MAC address respective to each of the multiple DL MU target STAs or an ID respective to each of the multiple DL MU target STAs (AID(association identifier), PAID(partial association identifier)).
  • identification information respective to each of the multiple DL MU target STAs e.g., MAC address respective to each of the multiple DL MU target STAs or an ID respective to each of the multiple DL MU target STAs (AID(association identifier), PAID(partial association identifier)).
  • a RA field of the RTS frame 400 may have a format for including identification information respective to multiple DL MU target STAs instead of the identification information of one DL MU target STA.
  • the legacy STA may decode only the duration field, which is located before the RA field of the RTS frame 400 , so as to configure the NAV. Therefore, even in case the format respective to the RA field of the RTS frame 400 is changed, there may be no impact (or influence) on the legacy STA.
  • Each the multiple DL MU target STAs may sequentially transmit CTS frames 410 , 420 , 430 , and 440 in response to the RTS frame 400 .
  • the transmission order of the CTS frames 410 , 420 , 430 , and 440 of the multiple DL MU target STAs may be decided based on diverse methods. For example, the transmission order of the CTS frames 410 , 420 , 430 , and 440 of the multiple DL MU target STAs may be decided based on an index (or position) of the allocated subband.
  • a frequency bandwidth of 20 MHz may include 4 subbands, and a subband index respective to each of the 4 subbands may correspond to Subband 1 , Subband 2 , Subband 3 , and Subband 4 .
  • each of STA 1 , STA 2 , STA 3 , and STA 4 may sequentially transmit CTS frames 410 , 420 , 430 , and 440 .
  • STA 1 receives the RTS frame 400 , and, after a SIFS (short interframe space), STA 1 may transmit CTS Frame 1 410 to the AP. Thereafter, STA 2 , STA 3 , and STA 4 may sequentially transmit CTS Frame 2 420 , CTS Frame 3 430 , and CTS Frame 4 440 . More specifically, STA 2 monitors the transmission of CTS Frame 1 410 performed by STA 1 , and, then, after a SIFS after the transmission of CTS Frame 1 410 , STA 2 may transmit CTS Frame 2 420 .
  • SIFS short interframe space
  • STA 2 decides the transmission timing of CTS Frame 2 420 , and, then, STA 2 may transmit CTS Frame 2 420 at the decided transmission timing of CTS Frame 2 420 .
  • the transmission order of the CTS frames 410 , 420 , 430 , and 440 of the multiple DL MU target STAs may be decided based on an order of identification information respective to each of the multiple DL MU target STAs included in the RA field of the RTS frame 400 .
  • a plurality of bits configuring the RA field of the RTS frame 400 may sequentially indicate STA 1 , STA 2 , STA 3 , and STA 4 as the multiple DL MU target STAs.
  • each of STA 1 , STA 2 , STA 3 , and STA 4 may transmit CTS Frame 1 410 , CTS Frame 2 420 , CTS Frame 3 430 , and CTS Frame 4 440 to the AP by the order of STA 1 , STA 2 , STA 3 , and STA 4 .
  • the CTS frames 410 , 420 , 430 , and 440 may not include a TA(transmitter address) field including identification information of the transmitting end (or each of the multiple DL MU target STAs transmitting the CTS frames 410 , 420 , 430 , and 440 ).
  • the AP may acquire information respective to the DL MU STAs, which have transmitted the CTS frames 410 , 420 , 430 , and 440 based on the pre-decided transmission order of the CTS frames 410 , 420 , 430 , and 440 or the reception timing of the CTS frames 410 , 420 , 430 , and 440 .
  • the RTS frame 400 and the CTS frames 410 , 420 , 430 , and 440 may be transmitted through the entire bandwidth for the transmission of the RTS frame 400 and the CTS frames 410 , 420 , 430 , and 440 . More specifically, instead of being transmitted based on OFDMA, the RTS frame 400 and the CTS frames 410 , 420 , 430 , and 440 may be transmitted through an entire bandwidth that is allocated based on one PPDU. The format of such PPDU may be expressed by using the term non-duplicate PPDU format. Alternatively, the RTS frame and the CTS frames may also be transmitted through multiple channels based on a duplicate PPDU format.
  • the duplicate PPDU format may replicate a PPDU format being transmitted through a neighboring channel (or primary channel) (20 MHz) and may then be transmitted through a bandwidth exceeding 20 MHz (e.g., 40 MHz, 80 MHz, 160 MHz, 80 MHz+80 MHz, and so on).
  • a neighboring channel or primary channel
  • 20 MHz e.g. 40 MHz, 80 MHz, 160 MHz, 80 MHz+80 MHz, and so on.
  • the RTS PPDU and CTS PPDU of the non-duplicate PPDU format or the duplicate PPDU format may be transmitted to at least one STA (or AP) through at least one space time stream.
  • the RTS frame 400 may also be transmitted based on a DL MU transmission method. More specifically, in case of the RTS frame 400 , different RTS frames 400 may be respectively transmitted to multiple STAs through different space time streams based on the DL MU MIMO transmission. Alternatively, different RTS frames 400 may be respectively transmitted to multiple STAs through different frequency resources (or subbands, channels) based on DL MU OFDMA. In this case, the RTS frames 400 being transmitted through different space time streams or different frequency resources may not include the same information. More specifically, the AP may respectively transmit each of the multiple RTS frames 400 to each of the STAs based on the DL MU transmission. For example, a RTS frame 400 that is being transmitted through a specific space time stream or a specific frequency resource based on the DL MU transmission may only indicate a specific STA that is to receive the RTS frame 400 through a specific frequency resource.
  • the AP may respectively receive CTS frames 410 , 420 , 430 , and 440 from multiple DL MU target STAs and may transmit downlink frames (or downlink data frames or downlink management frames) based on the DL MU OFDMA transmission.
  • the AP may transmit each of the multiple downlink frames (downlink PPDUs) to each of the multiple DL MU target STAs within the overlapping time resource through the subbands allocated to each of the multiple DL MU target STAs.
  • downlink PPDUs downlink PPDUs
  • the AP may transmit Downlink Frame 1 (Downlink PPDU 1 ) 450 to STA 1 through Subband 1 , the AP may transmit Downlink Frame 2 (Downlink PPDU 2 ) 460 to STA 2 through Subband 2 , the AP may transmit Downlink Frame 3 (Downlink PPDU 3 ) 470 to STA 3 through Subband 3 , and the AP may transmit Downlink Frame 4 (Downlink PPDU 4 ) 480 to STA 4 through Subband 4 .
  • Downlink PPDU 1 Downlink PPDU 1
  • the AP may transmit Downlink Frame 2 (Downlink PPDU 2 ) 460 to STA 2 through Subband 2
  • the AP may transmit Downlink Frame 3 (Downlink PPDU 3 ) 470 to STA 3 through Subband 3
  • the AP may transmit Downlink Frame 4 (Downlink PPDU 4 ) 480 to STA 4 through Subband 4 .
  • FIG. 5 illustrates a concept diagram of a RTS frame according to an exemplary embodiment of the present invention.
  • the RTS frame may include a frame control field 500 , a duration field 510 , a RA(receiver address) field 520 , a TA(transmitter address) field 530 , and a FCS(frame check sequence) field 540 .
  • the frame control field 500 may include information for indicating the RTS frame.
  • the duration field 510 may include duration information for the transmission of a CTS frame, an uplink transmission indication frame, uplink frames respective to each of the multiple STAs, and an ACK frame. As described in the exemplary embodiment of the present invention, in case multiple CTS frames are sequentially received, the duration field 510 may include duration information that has considered the reception of multiple CTS frames.
  • the RA field 520 may include information indicating the DL MU target STA that is to transmit the CTS frame.
  • the RA field 520 may correspond to a field of 48 bits (6 octets). In case a maximum of 4 STAs support the UL MU transmission, among the 48 bits, 12 bits may be allocated in order to identify one STA.
  • the DL MU target STA may transmit the CTS frame while considering the order of the identifiers of the multiple STA, which are included in the received RA field.
  • the TA field 530 may include an address of the AP transmitting the RTS frame.
  • the FCS field 540 may include information for verifying the validity of a frame.
  • FIG. 6 and FIG. 7 disclose collisions that may occur between a BSS supporting the DL MU OFDMA transmission and a neighboring BSS that does not support the DL MU OFDMA transmission.
  • FIG. 6 illustrates a concept diagram showing a collision between a BSS supporting DL MU OFDMA transmission and a BSS not supporting DL MU OFDMA transmission.
  • AP 1 615 may transmit a RTS frame to multiple DL MU target STAs (STA 1 610 , STA 2 620 , STA 3 630 , and STA 4 640 ), and, in response to the RTS frame, AP 1 615 may receive a CTS frame from each of the multiple DL MU target STAs (STA 1 610 , STA 2 620 , STA 3 630 , and STA 4 640 ).
  • STA 5 650 may receive a RTS frame, which is transmitted by AP 1 615 , and may then configure a NAV.
  • STA 6 660 may only receive the CTS frame, which was transmitted by STA 4 640 . If STA 6 acquires the authority to access a medium through a back-off procedure prior to the reception of the CTS frame of STA 6 660 (or the transmission of the CTS frame of STA 4 ), STA 6 660 may transmit an uplink frame to AP 2 625 without configuring a NAV. In this case, a collision may occur between the uplink frame transmitted by STA 6 660 and the downlink frame transmitted by AP 1 615 in the receiving end of STA 4 640 .
  • FIG. 7 illustrates a concept diagram showing a collision between a BSS supporting DL MU OFDMA transmission and a BSS not supporting DL MU OFDMA transmission.
  • AP 1 715 may transmit a RTS frame to multiple DL MU target STAs (STA 1 710 , STA 2 720 , STA 3 730 , and STA 4 740 ), and, in response to the RTS frame, AP 1 715 may receive a CTS frame from each of the multiple DL MU target STAs (STA 1 710 , STA 2 720 , STA 3 730 , and STA 4 740 ).
  • STA 5 750 may receive a RTS frame, which is transmitted by AP 1 715 , and may then configure a NAV.
  • AP 2 725 may be incapable of receiving the RTS frame transmitted from AP 1 715 , and AP 2 725 may receive the CTS frame transmitted by STA 4 740 .
  • AP 2 725 acquires the authority to access a medium through a back-off procedure before receiving the CTS frame (or before the transmission of the CTS frame by STA 4 740 )
  • AP 2 725 may transmit a downlink frame to STA 6 720 without configuring a NAV. In this case, a collision may occur between the downlink frame transmitted by AP 2 725 and the downlink frame transmitted by AP 1 715 in the receiving end of STA 4 740 .
  • the exemplary embodiment of the present invention discloses a method for preventing the problem of collision between frames shown in FIG. 6 and FIG. 7 .
  • BSS 1 may indicate a BSS that supports the DL MU OFDMA
  • BSS 2 may indicate a BSS that does not support the DL MU OFDMA and that is adjacent to BSS 1 or that overlaps with BSS 1 .
  • FIG. 8 illustrates a medium protection method according to an exemplary embodiment of the present invention.
  • FIG. 8 discloses a method for deciding whether or not the DL MU target STA, which is included in BSS 1 , should transmit a CTS frame in response to the RTS frame based on the frame that is being transmitted by BSS 2 .
  • AP 1 815 may transmit the RTS frame to multiple DL MU target STAs.
  • a DL MU target STA which has detected the occupation of the medium by the AP or STA included in BSS 2 , may not transmit a CTS frame.
  • STA 4 840 may receive the RTS frame that is transmitted by STA 5 850 . In this case, STA 4 840 may not transmit a CTS frame in response to the RTS frame, which is transmitted by AP 1 815 . Alternatively, STA 4 840 may transmit a CTS frame. However, the CTS frame may include additional information indicating that the reception of a downlink frame cannot be performed (or the reception of the downlink frame is not available).
  • AP 1 815 fails to receive a CTS frame from STA 4 840 , it will be apparent that a downlink frame cannot be transmitted to STA 4 840 through any one of the subbands included in the entire band (e.g., 20 MHz) that has transmitted the RTS frame. More specifically, in BSS 2 , since the legacy STA (STA 5 850 ) and AP 2 825 performs communication through a minimum band of 20 MHz, a collision between the frames may occur regardless of the subband, which is included within 20 MHz, that is used by AP 1 815 to transmit a downlink frame to STA 4 . Therefore, AP 1 cannot transmit a downlink frame to STA 4 .
  • FIG. 8 discloses a method for not transmitting a CTS frame, in a case when a DL MU STA (STA 4 840 ), which has received the RTS frame transmitted by AP 1 815 , detects a RTS frame being transmitted by STA 5 850 , which is included in BSS 2 , before transmitting the CTS frame.
  • STA 4 840 a DL MU STA
  • the STA 4 840 may detect a CTS frame of STA 5 850 being transmitted as a response to the RTS frame, which is transmitted by AP 2 825 , and an ACK frame of STA 5 850 being transmitted as a response to the downlink frame, which is transmitted by AP 2 825 , and may not transmit the CTS frame to AP 1 815 .
  • the AP may transmit a downlink frame to the remaining DL MU target STAs excluding the DL MU target STA that does not transmit a CTS frame based on DL MU OFDMA.
  • the AP may transmit a downlink frame to the remaining DL MU target STAs excluding the DL MU target STA that does not transmit a CTS frame based on DL MU OFDMA.
  • AP 1 815 may respectively transmit Downlink Frame 1 to STA 1 810 , Downlink Frame 2 to STA 2 820 , and Downlink Frame 3 to STA 3 830 through the remaining subbands (Subbands 1 , 2 , and 3 ) excluding Subband 4 based on DL MU OFDMA.
  • FIG. 8 discloses a method according to which the DL MU target STA detects a frame being transmitted by a STA included in BSS 2 and does not transmit a CTS frame.
  • the DL MU target STA may also detect a frame being transmitted by an AP included in BSS 2 and may not transmit a CTS frame.
  • the AP may transmit a RTS(request to send) for medium protection to a first STA(station) set, and the AP may sequentially receive a CTS(clear to send) from each of the multiple STAs included in a second STA set in response to the RTS frame.
  • the first STA set may include DL MU target STAs that are indicated based on the RTS frame, which is transmitted by the AP.
  • the RA field of the RTS frame may include identification information of the multiple STAs included in the first STA set.
  • the second STA set may include STAs that have transmitted a CTS frame to the AP.
  • the remaining STAs that are included in the first STA set and yet not included in the second STA set may correspond to DL MU target STAs, which have detected the occupation of the medium by another AP or another STA, and which may configure a NAV and not transmit the CTS frame.
  • the AP may respectively transmit each of the multiple PPDUs to each of the multiple STAs being included in the second STA set through each of the multiple subbands for each of the multiple STAs within the overlapping time resource.
  • the AP may transmit data units including dummy signals through subbands that are allocated to the remaining STAs, which are included in the first STA set yet not included in the second STA set within the overlapping time resource.
  • the AP may also decide a transmission power respective to each of the multiple PPDUs while considering the size of the subbands being allocated to the remaining STAs, which are included in the first STA set yet not included in the second STA set within the overlapping time resource. This will be described later on in more detail.
  • FIG. 9 illustrates a medium protection method according to an exemplary embodiment of the present invention.
  • FIG. 9 discloses a method for deciding whether or not the DL MU target STA, which is included in BSS 1 , should transmit a CTS frame in response to the RTS frame based on the frame that is being transmitted by BSS 2 .
  • the AP may transmit the RTS frame to multiple DL MU target STAs.
  • a DL MU target STA which has detected the occupation of the medium by the AP or STA included in BSS 2 , may not transmit a CTS frame.
  • STA 4 940 may receive the RTS frame that is transmitted by AP 2 925 . In this case, STA 4 940 may not transmit a CTS frame in response to the RTS frame, which is transmitted by AP 1 915 . Alternatively, STA 4 940 may transmit a CTS frame. However, the CTS frame may include additional information indicating that the reception of a downlink frame cannot be performed (or the reception of the downlink frame is not available). In case AP 1 915 fails to receive a CTS frame from STA 4 940 , it will be apparent that a downlink frame cannot be transmitted to STA 4 940 .
  • FIG. 9 discloses a method for not transmitting a CTS frame, in a case when a DL MU STA, which corresponds to STA 4 940 , that has received the RTS frame transmitted by AP 1 915 , detects a RTS frame being transmitted by AP 2 925 , which is included in BSS 2 , before transmitting the CTS frame.
  • STA 4 940 may detect a CTS frame of AP 2 925 being transmitted as a response to the RTS frame, which is transmitted by STA 5 950 , and an ACK frame of AP 2 925 being transmitted as a response to the downlink frame, which is transmitted by STA 5 950 , and may not transmit the CTS frame.
  • the AP may transmit a downlink frame to the remaining DL MU target STAs excluding the DL MU target STA that does not transmit a CTS frame based on DL MU OFDMA.
  • FIG. 10 illustrates a concept diagram of a downlink frame being transmitted based on DL MU OFDMA according to an exemplary embodiment of the present invention.
  • FIG. 10 discloses a method according to which the AP transmit a downlink frame based on DL MU OFDMA, in a case when a DL MU target STA that has not transmitted a CTS frame exists among the multiple DL MU target STAs.
  • the AP may transmit a RTS frame 1000 to DL MU target STAs (STA 1 , STA 2 , STA 3 , and STA 4 ).
  • the AP may receive CTS Frame 1 1010 , CTS Frame 2 1020 , and CTS Frame 3 1030 , which are respective transmitted by STA 1 , STA 2 , and STA 3 , and the AP may not receive CTS Frame 4 from STA 4 1040 .
  • the AP may transmit a downlink frame to each of STA 1 , STA 2 , and STA 3 with the exception for STA 4 .
  • the AP may transmit Downlink Frame 1 (Downlink PPDU 1 ) 1040 to STA 1 through Subband 1 , may transmit Downlink Frame 2 (Downlink PPDU 2 ) 1050 to STA 2 through Subband 2 , and may transmit Downlink Frame 3 (Downlink PPDU 3 ) 1060 to STA 3 through Subband 3 , based on the DL MU OFDMA transmission with the overlapping time resource.
  • the AP may not transmit Downlink Frame 4 (Downlink PPDU 4 ) through Subband 4 .
  • FIG. 11 illustrates a concept diagram of a downlink frame being transmitted based on DL MU OFDMA according to an exemplary embodiment of the present invention.
  • FIG. 11 discloses a method according to which the AP transmit a downlink frame based on DL MU OFDMA, in a case when a DL MU target STA that has not transmitted a CTS frame exists among the multiple DL MU target STAs.
  • the AP may transmit a RTS frame 1100 to DL MU target STAs (STA 1 , STA 2 , STA 3 , and STA 4 ).
  • the AP may receive CTS Frame 1 1110 , CTS Frame 2 1120 , and CTS Frame 3 1130 , which are respective transmitted by STA 1 , STA 2 , and STA 3 , and the AP may not receive CTS Frame 4 from STA 4 .
  • the detection levels of the STAs detecting downlink frames, which are being transmitted based on DL MU OFDMA may be interpreted differently.
  • the STA may differently determine whether the medium is busy or idle in accordance with the number of multiple subframes being transmitted based on DL MU OFDMA.
  • the STA may determine that the medium is busy.
  • the size of the power, which is sensed within the medium in accordance with the number of multiple subframes, may vary, and the interpretation of the state of the medium respective to the STAs may vary accordingly.
  • the transmission power of the downlink frame may be adjusted in accordance with the number of multiple subframes being transmitted based on DL MU OFDMA.
  • the transmission power for transmitting Downlink Frame 4 (Downlink PPDU 4 ) through Subband 4 may be used for the transmission of another one of Downlink Frame 1 to Downlink Frame 3 (Downlink PPDU 1 1140 to Downlink PPDU 3 1160 ). More specifically, the transmission power for each of Downlink PPDU 1 1140 to Downlink PPDU 3 1160 may be increased while considering the transmission power of Downlink PPDU 4 .
  • the AP may also transmit a data unit 1170 including a dummy signal through Subband 4 . More specifically, the AP may determine whether or not to include a dummy signal based on whether or not the CTS frame has been received from the DL MU target STA.
  • STA 4 which detects a frame that is being transmitted by the STA or AP included in BSS 2 , and which does not transmit a CTS frame to the AP, may already be in a state of configuring a NAV based on a frame, which is transmitted by the STA or AP included in BSS 2 . Therefore, the transmission of the dummy signal may not cause any influence (or impact) of the performance of STA 4 .
  • FIG. 12 illustrates a concept diagram of a downlink frame being transmitted based on DL MU OFDMA according to an exemplary embodiment of the present invention.
  • a CTS frame may be transmitted based on a MBSFN(multicast broadcast single frequency network) method.
  • the AP may transmit a RTS frame 1200 to DL MU target STAs (STA 1 , STA 2 , STA 3 , and STA 4 ).
  • a DL MU target STA may transmit a CTS frame 1210 to the AP by using the MBSFN method. More specifically, the CTS frame 1210 that is being transmitted by the DL MU target STA may include the same data and may be transmitted from an overlapping time resource and an overlapping frequency resource (or within the same (or overlapping) subband). In FIG. 11 , a case when STA 4 does not transmit CTS Frame 4 will be assumed.
  • the RA field of the CTS frame 1210 may include identification information (e.g., MAC address) of a transmitting end (e.g., AP) of the RTS frame 1200 being included in the TA field of the RTS frame 1200 .
  • identification information e.g., MAC address
  • AP transmitting end
  • Each of STA 1 to STA 3 may receive the RTS frame 1200 and may transmit a CTS frame 1210 including the same data in each field after a SIFS.
  • the CTS frame 1210 may not include a field including information on the address of a transmitting end (e.g., TA(transmitter address) field), which has transmitted the CTS frame 1210 . Therefore, the AP may be incapable of knowing by which DL MU target STA, among the multiple DL MU target STAs that have received the RTS frame 1200 , the CTS frame 1210 has been transmitted.
  • the AP may transmit a downlink frame to all of the multiple DL MU target STAs, which are targeted by the RTS frame 1200 , without considering the DL MU target STA that has not transmitted the CTS frame 1210 .
  • the AP may also transmit a downlink frame to STA 4 , which has not transmitted the CTS frame 1210 , through Subband 4 .
  • the CTS frame 1210 may also be transmitted for the NAV configuration of another STA excluding the DL MU target STAs.
  • the AP may transmit a RTS(request to send) frame for medium protection to a first STA(station) set.
  • the RA(receiver address) field of the RTS frame being transmitted by the AP may include identification information respective to each of the multiple STAs being included in the first STA set.
  • the AP may receive a CTS frame from each of the multiple STAs being included in the second STA set within an overlapping time resource and an overlapping frequency resource, and, herein, the second STA set may be included in the first STA set.
  • the first STA set may include DL MU target STAs from which the AP of the RTS frame intends to receive the CTS frame (or to which the AP intends to transmit a downlink frame).
  • the second STA set may include STAs transmitting the CTS frame as a response to the RTS frame.
  • the AP may transmit each of the multiple PPDUs to each of the multiple STAs included in the first STA set through each of the multiple subbands for each of the multiple STAs being included in the first STA set within an overlapping time resource.
  • the AP may transmit downlink frames (downlink PPDUs) 1250 , 1260 , 1270 , and 1280 to all of the multiple DL MU target STAs based on the DL MU OFDMA transmission without considering whether or not the reception of the CTS frame 1210 , which is transmitted by all of the multiple DL MU target STAs that are targeted by the RTS frame 1200 , is successful.
  • downlink PPDUs downlink PPDUs
  • STA 4 which detects the frame being transmitted by the STA (e.g., STA 5 in FIG. 8 ) or the AP (e.g., AP 2 in FIG. 9 ) that is included in BSS 2 and does not transmit a CTS frame to the AP, may already be in a state of configuring a NAV based on a frame, which is transmitted by the STA or AP included in BSS 2 . Therefore, the transmission of the Downlink Frame 4 may not cause any influence (or impact) of the performance of STA 4 .
  • the frame being transmitted by the STA (e.g., STA 5 in FIG. 8 ) or the AP (e.g., AP 2 in FIG. 9 ) that is included in BSS 2 does not cause any interference on the DM MU target STA receiving a downlink frame and being included in the BSS.
  • the method disclosed in FIG. 12 may effectively support the NAV configuration of a legacy STA. Therefore, this method may be more effective in a BSS or ESS(extended service set), wherein a large number of legacy STAs exist.
  • FIG. 13 illustrates a concept diagram showing a downlink frame transmission method of an AP according to an exemplary embodiment of the present invention.
  • FIG. 13 discloses a medium protection method.
  • a NAV configuration respect to another STA instead of a hidden node (or hidden position) may be supported.
  • the PPDU carrying (or containing (or including) a frame may include a legacy part and a non-legacy part.
  • the legacy part may include L-STF 1310 , L-LTF 1320 , and L-SIG 1330 .
  • the non-legacy part 1340 may include a PPDU header (e.g., HE-STF, HE-LTF, and HE-SIG) for a non-legacy wireless LAN system that supports DL MU OFDMA and UL MU OFDMA (or UL MU MIMO), and a MPDU(MAC protocol data unit) (or PSDU(physical layer service data unit)).
  • the non-legacy part 1340 may also be expressed by using the term HEW part (or HE part).
  • the non-legacy part 1340 may include HE-SIG A, HE-STF, HE-LTF, and HE-SIG B, which will be described later on in more detail.
  • the legacy part 1310 , 1320 , and 1330 may be transmitted through a 20 MHz band and may be decoded by a legacy STA.
  • the non-legacy part 1340 may be transmitted to multiple STAs based on DL MU OFDMA based on a subband granularity that is smaller than 20 MHz (e.g., 5 MHz).
  • the legacy STA may receive the legacy part 1310 , 1320 , and 1330 , may configure a NAV based on a legacy field (e.g., length information, MCS information, and so on, included in the legacy field), and may not perform decoding on the non-legacy part 1340 .
  • a legacy field e.g., length information, MCS information, and so on, included in the legacy field
  • the STA may convert the legacy part 1310 , 1320 , and 1330 , which is being transmitted through a 20 MHz band, based on 64FFT, and may perform decoding on the converted part, and the STA may also perform decoding on the remaining non-legacy part 1340 , thereby being capable of receiving data.
  • the legacy STA may not successfully perform decoding starting from the non-legacy part 1340 . Accordingly, the legacy STA may know that the received PPDU correspond to a PPDU that is not supported (that the PPDU does not correspond to its packet). Alternatively, a most temporally preceding block within the non-legacy part 1340 (or a most temporally preceding OFDM symbol or most temporally preceding field within the non-legacy part 1340 ) may be transmitted through 20 MHz so that the constellation rotation rule can be applied.
  • a PPDU format (or a version of the wireless LAN system that has transmitted the PPDU) may be detected based on the constellation that was used for generating a modulation symbol that is being transmitted through the OFDM symbol. For example, a symbol that is being transmitted within a last OFDMA symbol (or last field) of the legacy part may be generated based on a first constellation, and a first OFDMS symbol (or first field) of the non-legacy part may be generated based on a second constellation.
  • the first OFDM symbol or first field of the non-legacy part 1340 may be transmitted from a 20 MHz band.
  • the first OFDM symbol for first field of the non-legacy part 1340 may correspond to a common non-legacy block (or HE block) of 20 MHz.
  • the first field of the non-legacy part may correspond to HE-STF or HE-LTF for differentiating the bandwidth or may correspond to HE-SIG including identification information of multiple STAs that are to receive downlink frames.
  • FIG. 14 illustrates a concept diagram showing a PPDU format for transmitting a frame according to an exemplary embodiment of the present invention.
  • FIG. 14 discloses a PPDU format according to an exemplary embodiment of the present invention.
  • the PPDU format disclosed in FIG. 14 may carry or include a downlink frame, which is transmitted based on the DL MU OFDMA transmission.
  • the RTS frame and the CTS frame according to the exemplary embodiment of the present invention may also be transmitted through the PPDU format, which is disclosed in FIG. 14 .
  • the PHY header of the downlink PPDU may include a L-STF(legacy-short training field), a L-LTF(legacy-long training field), a L-SIG(legacy-signal), a HE-SIG A(high efficiency-signal A), a HE-STF(high efficiency-short training field), a HE-LTF(high efficiency-long training field), and a HE-SIG B(high efficiency-signal-B).
  • the PHY header may be divided into a legacy part, which consists of a part up to L-SIG, and a HE(high efficiency) part (HE part), which consists of after the L-SIG.
  • the L-STF 1400 may include a short training OFDM symbol (short training orthogonal frequency division multiplexing symbol).
  • the L-STF 1400 may be used for frame detection, AGC(automatic gain control), diversity detection, and coarse frequency/time synchronization.
  • the L-LTF 1410 may include a long training OFDM symbol (long training orthogonal frequency division multiplexing symbol).
  • the L-LTF 1410 may be used for fine frequency/time synchronization and channel prediction.
  • the L-SIG 1420 may be used for transmitting control information.
  • the L-SIG 1420 may include information on data transmission rate, data length, and so on.
  • the legacy STA may configure a NAV based on the information included in L-SIG.
  • the HE-SIG A 1430 may include information for indicating the STA that is intended to receive the PPDU.
  • the HE-SIG A 1430 may include an identifier of a specific STA that is to receive the PPDU, information for indicating the group of the STA.
  • the HE-SIG A 1430 may also include resource allocation information respective to the STA.
  • the HE-SIG A 1430 may also include color bits information for BSS identification information, bandwidth information, tail bit, CRC bit, MCS(modulation and coding scheme) information respective to the HE-SIG B 1460 , information on the number of symbols for the HE-SIG B 1460 , and CP(cyclic prefix) (or GI(guard interval)) length information.
  • the HE-STF 1440 may be used for enhancing automatic gain control estimation in a MIMO(multiple input multiple output) environment or an OFDMA environment.
  • the HE-LTF 1450 may be used for estimating a channel in a MIMO environment or an OFDMA environment.
  • the HE-SIG B 1460 may include information on a length MCS of a PSDU(Physical layer service data unit) respective to each STA and tail bit, and so on. Additionally, the HE-SIG B 1460 may also include information on an STA that is to receive the PPDU, OFDMA based resource allocation information (or MU-MIMO information). In case the OFDMA based resource allocation information (or MU-MIMO related information) is included in the HE-SIG B 1460 , the resource allocation information may not be included in the HE-SIG A 1430 .
  • the size of the IFFT being applied to the HE-STF 1440 and the field after the HE-STF 1440 may be different from the size of the IFFT being applied to the field before the HE-STF 1440 .
  • the size of the IFFT being applied to the HE-STF 1440 and the field after the HE-STF 1440 may be four time larger than the size of the IFFT being applied to the field before the HE-STF 1440 .
  • the STA may receive the HE-SIG A 1430 and may receive indications on the reception of a downlink PPDU based on the HE-SIG A 1430 .
  • the STA may perform decoding based on a FFT size, which is changed starting from the HE-STF 1440 and the field after the HE-STF 1440 .
  • the STA may stop the decoding process and may configure a NAV(network allocation vector).
  • the CP(cyclic prefix) of the HE-STF 1440 may have a size that is larger than the CP(cyclic prefix) of another field, and, during such CP interval, the STA may change the FFT size so as to perform decoding on the downlink PPDU.
  • the order of the field configuring the format of the PPDU may vary.
  • the HE-SIG B 1415 of the HE part may be located immediately after the HE-SIG A 1405 .
  • the STA may perform decoding on the HE-SIG A 1405 and up to the HE-SIG B 1415 , so as to receive the required control information, and, then, the STA may configure the NAV.
  • the size of the IFFT being applied to the HE-STF 1425 and the field after the HE-STF 1425 may be different from the size of the IFFT being applied to the field before the HE-STF 1425 .
  • the STA may receive the HE-SIG A 1405 and the HE-SIG B 1415 .
  • the STA may change the FFT size starting from the HE-STF 1425 and may perform decoding on the PPDU.
  • the STA may configure a NAV(network allocation vector).
  • a PPDU format for DL MU transmission is disclosed.
  • the AP may transmit a downlink frame or a downlink PPDU to multiple STAs by using the PPDU format for DL MU transmission.
  • Each of the multiple downlink PPDUs may be respectively transmitted to each of the multiple STAs through different transmission resources (frequency resources or space time streams).
  • the field before the HE-SIG B 1445 may be transmitted in a duplicated format from transmission resources each being different from one another.
  • the HE-SIG B 1445 may be transmitted in an encoded format within the entire transmission resource.
  • the field after the HE-SIG B 1445 may include individual information for each of the multiple STAs receiving the PPDU.
  • a CRC respective to each field may be included in the PPDU.
  • a specific field included in the PPDU is encoded within the entire transmission resource and then transmitted, a CRC respective to each field may not be included in the PPDU. Accordingly, an overhead respective to the CRC may be reduced.
  • the HE-STF 1455 and the field after the HE-STF 1455 may be encoded based on an IFFT size that is different from the field before the HE-STF 1455 . Therefore, in case the STA receives the HE-SIG A 1435 and the HE-SIG B 1445 , and in case the STA receives an indication to receive the PPDU based on the HE-SIG A 1435 , the STA may change the FFT size starting from the HE-STF 1455 and may then perform decoding on the PPDU.
  • FIG. 15 illustrates a block diagram showing a wireless communication system in which the disclosure of this specification is implemented.
  • the wireless device 1500 may correspond to an AP 1500 or a non-AP STA (non-AP station) 1550 .
  • the AP 1500 includes a processor 1510 , a memory 1520 , and a RF unit (radio frequency unit) 1530 .
  • the RF unit 1530 is connected to the processor 1510 , thereby being capable of transmitting and/or receiving radio signals.
  • the processor 1510 implements the functions, processes, and/or methods proposed in the present invention.
  • the processor 1510 may be realized to perform the operations of the wireless device according to the above-described exemplary embodiments of the present invention.
  • the processor may perform the operations of the wireless device, which are disclosed in the exemplary embodiments of FIG. 1 to FIG. 14 .
  • the processor 1510 may be configured to transmit a RTS(request to send) frame for medium protection to a first STA(station) group and to sequentially receive CTS(clear to send) frames from each of multiple STAs being included in a second STA set as a response to the RTS frame. And, the processor 1510 may also be configured to respectively transmit each of multiple PPDUs (physical layer protocol data unit) to each of the multiple STAs through each of multiple subbands for each of the multiple STAs within an overlapping time resource. The second STA set may be included in the first STA set.
  • PPDUs physical layer protocol data unit
  • the STA 1550 includes a processor 1560 , a memory 1570 , and a RF unit (radio frequency unit) 1580 .
  • the RF unit 1580 is connected to the processor 1560 , thereby being capable of transmitting and/or receiving radio signals.
  • the processor 1560 implements the functions, processes, and/or methods proposed in the present invention.
  • the processor 1560 may be realized to perform the operations of the wireless device according to the above-described exemplary embodiments of the present invention.
  • the processor may perform the operations of the wireless device, which are disclosed in the exemplary embodiments of FIG. 1 to FIG. 14 .
  • the processor 1560 may be implemented to receive a RTS frame from the AP and to transmit the CTS frame at a transmission timing, which is decided based on a position within the frequency resource of a subband for the STA.
  • the processor 1510 and 1560 may include an ASIC(application-specific integrated circuit), another chip set, a logical circuit, a data processing device, and/or a converter converting a baseband signal and a radio signal to and from one another.
  • the memory 1520 and 1570 may include a ROM(read-only memory), a RAM(random access memory), a flash memory, a memory card, a storage medium, and/or another storage device.
  • the RF unit 1530 and 1580 may include one or more antennas transmitting and/or receiving radio signals.
  • the above-described method may be implemented as a module (process, function, and so on) performing the above-described functions.
  • the module may be stored in the memory 1520 and 1570 and may be executed by the processor 1510 and 1560 .
  • the memory 1520 and 1570 may be located inside or outside of the processor 1510 and 1560 and may be connected to the processor 1510 and 1560 through a diversity of well-known means.

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US10602546B2 (en) 2020-03-24
WO2015126049A9 (fr) 2016-10-13
EP3110035A4 (fr) 2017-10-25
EP3110035A1 (fr) 2016-12-28
KR101919392B1 (ko) 2019-02-08
US20170013645A1 (en) 2017-01-12
US20180368185A1 (en) 2018-12-20

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